1. Field of the Invention
The invention relates to a light emitting control device and method thereof for a light emitting diode print head and, more particularly, to a light emitting control device and method thereof capable of effectively enhancing a light emitting time of a light emitting diode print head.
2. Description of the Prior Art
A printer is a computer output apparatus for printing text or image data stored in a computer on papers or other printing media. A Conventional printing process of the printer comprises following steps of: applying a charging voltage to a photosensitive member; exposing the photosensitive member by an optical writing device to form a latent image on a charged surface of the photosensitive member; developing the toner carried in a toner cartridge to the photosensitive member and the photosensitive member applies the toner to the latent image to form a toner image; transferring the toner image on the printing media (e.g. papers); and fusing the toner image onto the printing media by a fuser module. The optical writing device can be a laser light source or an LED light source.
Referring to FIG. 1, FIG. 1 is a timing chart of conventional printing technology. In the system of a conventional print head, a light emitting time of the print head is determined by a clock signal, a print data signal and a strobe signal. As shown in FIG. 1, Tp represents one period of the clock signal and Tms represents the maximum light emitting time. If there are n clock signals, a relation between Tp and Tms is as follows, Tms=Tp*n. Generally speaking, a band width of the strobe signal is determined by a number of the clock signals. Accordingly, the light emitting time is determined by the clock signals and the print data signal. However, the conventional printing technology will have the following problems. Although the print head is completely switched on within the length of the print data signal, the light emitting time is sometimes not sufficient so as to affect printing quality. Therefore, only the clock signals can be adjusted to solve the aforesaid problems.
If one desires to enhance the maximum light emitting time, reduction in the frequency of the clock signals for the print head is required. Several prior arts are disclosed as follows:
1) In case not to change the clock signals in the system, a frequency dividing method can be used. This method can be achieved by little modification of circuit design, but it can only be divided by a multiple of 2. Even if only little enhancement of the maximum light emitting time is required, time for transferring print data will increase a lot such as at least two times, such that the efficiency of the whole system will decrease.
2) In case not to change the clock signals, a circuit such as Phase-Locked Loop (PLL) circuit or any other circuits can be used, so as to arbitrarily change the output frequency of the clock signals. Accordingly, it can enhance the maximum light emitting time without increasing too much time for transferring print data. However, the circuit design will get complicated.
3) In case to change the clock signals for the whole system, the maximum light emitting time can be enhanced without additional circuit design. Since the clock signals in the system are changed, other control signals should also be changed and system parameters should also be reset. As a result, it will increase the complexity of firmware design.